Proper soil test data help to design a building foundation safely. Type of foundation and their depth directly depend on it. Before starting Structural Design, a proper soil investigation is required to know the soil properties which ultimately ensured the ultimate building safety.

Proper and accurate soil testing reduce the building cost. Without soil test, foundation designer may imply more factor of safety in foundation designing which may occur unusual cost of building. On the other hand, if soil not capable of carrying building loads, it’s may occur total building failure.

The total building structures stands on foundation soil. If soil bearing capacity is not adequate to carry building loads, the building may fully or partially collops. It may cause huge life risk and property loss. It is difficult to change the foundation strength of a complete building and costly task. So ensure accurate soil testing before building design.

Generally, a building may design for a certain services life of 80 to 100 years. If your superstructures are strong enough but foundation undergoes partial settlement or failure, it drastically impacts on your superstructures to imposed additional shear, moment and torsion. Resulting failure of buildings before it’s designed lifetime.

When a building stands on a soft soil, it must settle down after certain period of life. There are two types of settlements occur in Structures, a. Uniform Settlements b. Differential Settlements. Uniform settlements are less harmful, because the whole structures undergo to settle down uniformly. But the differential settlements are very vulnerable to any structures, as a portion of a structure settle down more than the other portion. In this case structural elements experienced additional moment, shear and torsional forces. Result in catastrophic failure of whole structure and case huge loss of property and lives. So, we should rest any time of structures in a hard layer of soil. A proper soil test and sub-soil investigation may resolve the all above issues.

Now a days, most of the high-rise buildings are consists of Two or More Basements parking. The construction of Multi basement building need deep excavation of foundation soil. The critical issues in such construction is negative pore water pressure and seepage which lead a basement construction to collapse of shore protection and side soil. Also, the negative pressure of soil is a vital issue in designing shear walls and basement slab. Accurately knowing the Ground Water Level from Soil Test Reports, a structural engineer can consider and take preventive measures against the above circumstances.

This is first step, while you are thinking for conduction geotechnical investigation at your proposed site. Existing old structures to be demolished and properly cleaned before starting works. If complete demolition not possible, then an open space of 5 feet by 5 feet to be created for placing soil test rig and tripods. Water requirement is a very essential pre-requisite during soli exploration. So nearby source of water selection is also a vital part of whole process. Any RCC floor found under in the boring points, must be completely removed before conducting boring work.

The properties of soil may very one location to adjacent location. So it is very crucial part to select the number of boring points depending the land size and shape. For very small sites like 2 katha to 3 katha land, at least 3 points soil tests are desirable. But for larger size of land, 1 point for every 1 katha land provides more accurate and relevant soil data from test results. Selection of bore hole locations also an important port. The building footprint and the uniform intensity of test points are considered as the vital issue for selection of wash boring locations.

The site mobilization includes the carrying of soil test equipment like drilling Rig, Casing Pipes, Drill Pipes, Soil Sampler , Auto Trip Hammer, Slurry Pump, Water Injector, Tripod, Vanilla Rope etc. The carrying of skilled labor and non-skilled labor are also part of site mobilization. Generally, the equipment and man power are carried through a 5 tons Pickup Van. Sometimes it is required stay the all manpower at site for many days. In this case temporary labor shed or Tabu in also considered as a part field mobilization.

Field SPT collections is the most important part in wash boring soil sampling method. In this process, wash boring is carried out at desired locations and SPT values are collected at each 5 feet depth up to desired SPT value. To collect the SPT value a soil sampler, named Split Spoon Sampler are attached with the drill pipe and placed at the desired level. An Auto Tripped Hammer of 63.5 kg in weight dropped repeatedly from the same fixed height of 30 inch until the sampler penetrate up to 6 inch is depth and the number of blows is recorded. This process continues to another two times to penetrate in total 18 inch depth and recorded the values separately.

Form the recorded SPT Values, the corrected SPT or SPT NValues are computed. Blows for first 6 inch penetration are treated as seating value and cannot be counted in calculation of SPT N Value. The rest 12 inch penetration blows are considered as the total SPT N Values. For very hard or rock type soils, 50 SPT N Vales are desirable. So, collection of SPT blows to be continued up to desirable depth where 50 SPT N Values are obtained.

In wash boring method, generally two types of samples are collected at different depth of a boring point. a) Disturbed Samples b) Undisturbed Samples. When the in-situ properties of soil samples are get disturbed is considered as disturbed soil samples and when these properties are remain same are called undisturbed samples. For collection of disturbed soil sample, Split Spoon Samplers are used. On the other hand undisturbed soil samples are collected using Piston Samplers.

The collected disturbed and undisturbed soil samples are transferred to soil test laboratory. The physical properties of soil samples are captured by an experienced Geotechnical Engineer. The mechanical properties are calculated by performing necessary lab test of all soil samples. The commonly used laboratory tests are Natural Moisture Content, Specific Gravity, Atterberg Limits, Soil Density, Grain Size Analysis, Hydrometer Test, Direct Shear Test, Unconfined Compression Test, Consolidation Test, Triaxial Shear Test etc.

The Lab Test Results are further analyzed by expert Geotechnical and Foundation Engineers. Final test result data sheets and necessary graphical presentations are prepared. From the data sheets, soil bearing capacity and other properties are calculated using different Formulas. The most commonly and widely used Formula is TARZAGI BEARING CAPACITY FORMULA. The factor of safety for soil bearing capacity is considered as 3. After compiling these all data, a Soil Test Report is prepared and supplied to the client duty signed by RAJUK Enlisted Foundation Engineer.